Superhydrophobic, superoleophobic coatings for the protection of silk textiles

The fabrication of protective coatings on silk with special properties is presented. A water soluble siloxane emulsion enriched with silica nanoparticles (7 nm) is sprayed on silk, without the use of any organic solvent. By adjusting the nanoparticle concentration, treated silk obtains (i) superhydrophobic and superoleophobic properties, as evidenced by the high static contact angles of water and oil droplets (>150°) and (ii) water and oil repellent properties, as supported by the corresponding low tilt contact angles (<7°). SEM images show that nanoparticles lead to the formation of microscale clusters with nanostructures, which in turn induce a surface roughness at the micrometer and nanometer scale. The produced coatings have practically no effect on the aesthetic appearance of silk dyed with natural dyes such as indigo, weld, turmeric, and cochineal. Finally, it is shown that the applied coatings can be totally removed from the silk substrate using compressed carbon dioxide, either in supercritical or liquid state, mixed with a small amount of methanol. Consequently, the suggested method is reversible and therefore it has the potential to be used for the protection of modern as well as historic textiles.